Optical fiber cables that include several optical fiber micromodules are known. For example, French Publication No. FR 2,665,266 A (and its counterpart U.S. Pat. No. 5,155,789) and French Publication No. FR 2,706,218 A (and its counterpart U.S. Pat. No. 5,671,312) disclose an optical fiber micromodule surrounded by a retaining jacket enclosing several fibers.
A micromodule telecommunication cable includes a plurality of optical fibers grouped in micromodules. A micromodule may contain about 2 to 24 fibers enclosed in a flexible retaining jacket. The jackets for retaining the micromodules and the jackets of optical fibers may be colored to facilitate location of the fibers in the cable, (e.g., during connection operations).
The micromodules are disposed in a central cavity of the cable such that the cable jacket surrounds the micromodules. The jacket of the cable may be polymeric, typically of polyethylene; it may be extruded during the formation of the cable as the fibers are gradually grouped into micromodules.
The cable jacket may also contain reinforcing members positioned longitudinally. Indeed, the jacket typically is formed of material that is moisture-resistant but sensitive to temperature changes and not mechanically rigid. The reinforcing members are thus used for limiting the deformations of the cable due to tensile forces, such as occur during the installation of the cable in a duct, and for limiting the axial deformations of the cable upon compression and expansion when the cable is subject to significant changes in temperature, (i.e., by compensating the compression or expansion forces induced by the jacket).
Telecommunication optical fiber cables are generally intended to be laid in ducts of metropolitan or long-distance transmission systems. To permit the cable to be laid in a duct, the cable should have robustness to withstand the traction and the mechanical stresses of the laying, and flexibility along at least one folding direction to allow it to be inserted into the ducts of the system. Further, a telecommunication cable should generally withstand conditions of use over a large temperature range (e.g., −40° C. to +60° C.), which may cause expansions and compressions in the cable jacket. With the reinforcing members of the cable, the mechanical stresses experienced by the cable during the laying in a duct may be absorbed and the optical fibers positioned in the cable may thereby be protected. Such reinforcing members may be located in the central area of the cable or at its periphery thereof.
With development of telecommunications optical fiber systems to the subscriber, commonly known as Fiber-to-the-Home (FTTH) or Fiber-to-the-Curb (FTTC), it is desirable to produce cables with sufficient capacity to contain numerous optical fibers. Such cables are intended to be installed in an aggressive urban environment, (e.g., sewers), where they should be capable of resisting rodents and corrosion. Moreover, such cables should also provide individual access to each micromodule for distribution in a given building. In particular, each micromodule picked up during a bypass operation should be able to be drawn over several tens of meters in order to reach an optical box for junction with a telecommunication system of a given building.
European Publication No. EP 1,052,533 A (and its counterpart U.S. Pat. No. 6,181,857) describe a method for accessing one or more optical fibers in a sheath disposed in a telecommunications cable. Two cut-outs are made in the sheath to create a first aperture through which a fiber is cut and a second aperture through which the cut fiber is drawn in order to be bypassed. This publication discloses an optical fiber cable having a jacket forming a cavity that contains a telecommunications core. The core is formed by a plurality of colored optical fiber buffer tubes or sheaths. This publication, however, fails to disclose the presence of any lubricant in the cavity.
French Publication No. 2,214,900 discloses a telecommunications cable that includes a central cavity enclosing several bundles of optical fibers. The core of the cable is surrounded by a protective jacket, a metal layer, and an external jacket. The optical fibers are in a stranded configuration.
European Publication No. EP 0,468,878 (and its counterpart U.S. Pat. No. 5,155,789) disclose a telecommunications cable that includes high-density groups of parallel optical fibers within a cavity. This publication fails to disclose the presence of any lubricant within the cable cavity.
U.S. Patent Publication No. 2006/147164 discloses a telecommunications cable that includes bundles of optical fibers arranged within an inner polyolefin tube. This publication explicitly teaches that optical fibers and microbundles should be SZ stranded.
U.S. Pat. No. 6,366,725 discloses a telecommunications cable that includes bundles of optical fibers, wherein the core is surrounded by an outer cladding made of stainless steel. The outer cladding is not located on the inner periphery of said jacket. This patent fails to disclose the presence of any lubricant within the cavity.
International Publication No. WO 2001/98810 A (and its counterpart U.S. Pat. No. 6,718,101) describe a continuously accessible optical fiber that is particularly suited for local subscriber loops and interior cablings. This cable includes a protective jacket surrounding an oval cavity that receives optical fiber micromodules. The disclosed cable may receive only about 12 to 96 optical fibers.
According to International Publication No. WO 2001/98810, its fibers are arranged in the cable so that they occupy the major portion of the cavity along the major axis but leave significant clearance in the minor axis of the cavity. This clearance allows changes in overlength of the fibers in the cable. The jacket includes reinforcing members positioned on either side of the cavity along the major axis. The cable is wound on a cable drum or bent during installation in a duct along the major axis, thereby benefiting from the large clearance in the minor axis. The optical fibers thus have a certain degree of freedom within the cavity of the cable, lessening stresses upon jacket lengthening, such as from tension or from thermal expansion or contraction. The jacket includes markings (i.e., colored thin lines, fracture initiations, or areas with thinner thickness) to indicate the areas where windows may be pierced for bypass operations. A first access window may thus be opened in order to section a given micromodule and a second access window is opened for extracting the micromodule selected for the bypass. This publication fails to disclose (i) any lubricant in the central cavity and (ii) a sheath on the inner periphery of the jacket.
Moreover, International Publication No. WO 2001/98810 discloses a cable that provides a bypass of a micromodule extracted from the cable over a few tens of centimeters to several meters, but it does not provide a bypass over several tens of meters. Further, the disclosed cable is not suitable for installation in an aggressive environment such as sewers. The disclosed elastomer cable jacket is not sufficient for ensuring the integrity of the optical fibers in an aggressive outdoor environment.
European Publication No. EP 0,240,165 A (and its counterpart U.S. Pat. No. 4,836,639) disclose a cable in which the optical fibers are positioned in parallel (i.e., not wound as helices or non-cabled). The optical fibers are then positioned in contact with the inner wall of the jacket. This publication proposes that the reinforcing members of the jacket be positioned in proximity to the fibers. The reinforcing members are thus located on the side interior to the curvature of the cable when the cable is wound or bent. A neutral axis or a zero stress line connects the reinforcing members and passes through the group of fibers. Thus, the fibers do not retract or lengthen when the cable is wound or unwound from a cable drum. Such an arrangement may only be applied in a cable that includes only a rather limited number of optical fibers. Moreover, this publication fails to disclose any lubricant in the central cavity.
French Publication No. FR 2,815,141 (and its counterpart U.S. Pat. No. 6,937,802) disclose a telecommunications cable in which super modules of optical fibers are located in a central cavity. This publication fails to disclose the presence of any lubricant in the central cavity and any sheath located on the inner periphery of the jacket.
There is a need, therefore, for an outdoor cable that has a large capacity (i.e., several hundred optical fibers), and that provides a bypass of one or several micromodules over several tens of meters.